18N to the left and up or down.
The net force in the x direction is 10N to the left.
30N left -20N right
Since the 15 force acts perpendicular to the 10 and 20N forces it acts in the y- axis.
Since it is the only force acting in the y direction the net force in the y direction is 15N.
Use pythagorus to find the resultant force.